Messages in this thread | | | From | Ard Biesheuvel <> | Date | Tue, 21 Jun 2022 18:27:39 +0200 | Subject | Re: [RFC][PATCH] ftrace,objtool: PC32 based __mcount_loc |
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On Fri, 17 Jun 2022 at 13:40, Mark Rutland <mark.rutland@arm.com> wrote: > > On Fri, Jun 17, 2022 at 01:24:53PM +0200, Peter Zijlstra wrote: > > > > Hi, > > > > I recently noticed that __mcount_loc is 64bit wide, containing absolute > > addresses. Since __mcount_loc is a permanent section (not one we drop > > after boot), this bloats the kernel memory usage for no real purpose. > > > > The below patch adds __mcount_loc_32 and objtool support to generate it. > > This saves, on an x86_64-defconfig + FTRACE, 23975*4 ~= 94K of permanent > > storage. > > We have a similar issue on arm64, which is exacerbated by needing ABS64 > relocations (24 bytes per entry!) adding significant bloat when FTRACE is > enabled. > > It'd be really nice if going forwards compilers could expose an option to > generate PC32/PREL32 entries directly for this. >
As opposed to generating absolute references today? Or as opposed to having to rely on our own tooling?
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